| Poly (lactic acid) is a well-kown polymer with good biological compatibility and biodegradability, which is being regarded as one of the best useful biodegradable materials and increasingly used as a biomaterial for temporary therapeutic application. PLA is usually obtained by polymerization of lactic acid or ring-opening polymerization of lactide.High viscosity average molecular weight PLA was prepared by ring-opening polymerization of lactide. This paper firstly have studied factors such as reactive temperature, variety and quantity of the catalysts which how to affect the yield of L-lactide, then various influencing factors on the preparation of PLA were studied, such as the polymerization temperature, the polymerization time and quantity of the catalyst. By volumes of experiments we obtained the best parameters of PLA polymerization, for L-lactode: the polymerization temperature is 140℃,the polymerization time is 36 hours,the dosage of Sn(Oct)2 is 0．03%(by weight); for DL-lactide, the polymerization temperature is 165℃,the polymerization time is 46 hours and the dosage of Sn(Oct)2 is 0．03%, then,the viscosity average molecular weight of PLLA ,PDLLA reached 2×105 and 1．9×105The results showed that the depolymerization temperature had badly influence on the yield of L-lactide, when the temperature exceeded 230℃, we obtained DL-lactide instead of L-lactide. Variety and quantity of the catalysts had marked influence on the yield of L-lactide, whith 2%(based on total mass of reactants) ZnO as catalyst, the yield of L-lactide reached 47%. The graph of TG showed that the thermal stability of PLLA is better than PDLLAs thermal stability, further study also showed that the speed of PDLLA biodegradation is higher than the speed of PLLA.
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